SOLUTION: Determine the sum of the geometric series 3 + 6 + 12 + . . . + 768.

Algebra ->  Sequences-and-series -> SOLUTION: Determine the sum of the geometric series 3 + 6 + 12 + . . . + 768.      Log On


   

Question 412045: Determine the sum of the geometric series 3 + 6 + 12 + . . . + 768.
Answer by ewatrrr(24785) About Me  (Show Source):
You can put this solution on YOUR website!


Hi

Geometric Series

a%5Bn%5D+=+a%5B1%5D%2Ar%5E%28n-1%29

768=+3%2A2%5E%28n-1%29 

256 = 2^(n-1) 

 2^8 = 2^(n-1)

   8 = n-1

   n = 9

sum%28+a%5Bi%5D%2C+i=1%2C+infinity+%29 = a(1-r^n)/(1-r)

sum%28+a%5Bi%5D%2C+i=1%2C+9+%29 = 3(1-2^9)/(1-2) = 3 * -511/-1 = 1533